As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent charge retention and service-life characteristics, which has been widely used as an energy source for various electronic products as well as mobile devices.
Based on the appearance thereof, a lithium secondary battery may be classified as a cylindrical battery, a prismatic battery, or a pouch-shaped battery. Based on the type of an electrolyte, a lithium secondary battery may be also classified as a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery.
A recent trend in the miniaturization of mobile devices has increased the demand for a prismatic battery or a pouch-shaped battery, which has a small thickness. In particular, much interest is currently focused on such a pouch-shaped battery because it is easy to modify the shape of the pouch-shaped battery, the manufacturing cost of the pouch-shaped battery is low, and the pouch-shaped battery is lightweight.
In general, a pouch-shaped battery is a battery having an electrode assembly and an electrolyte in a pouch-shaped battery case, made of a laminate sheet including a resin layer and a metal layer, in a sealed state. The electrode assembly mounted in the battery case is configured in a jelly-roll (wound) type structure, a stacked type structure, or a combination (stacked/folded) type structure.
FIG. 1 is a view typically showing the structure of a pouch-shaped secondary battery including a stacked type electrode assembly. Referring to FIG. 1, a pouch-shaped secondary battery 10 is configured to have a structure in which an electrode assembly 30, including cathodes, anodes, and separators disposed respectively between the cathodes and the anodes, is mounted in a pouch-shaped battery case 20 in a sealed state such that two electrode leads 40 and 41 electrically connected to cathode and anode tabs 31 and 32 of the electrode assembly 30 are exposed to the outside.
The battery case 20 includes a case body 21 having a depressed receiving part 23, in which the electrode assembly 30 is located, and a cover 22 integrally connected to the case body 21.
The battery case 20 is made of a laminate sheet including an outer resin layer 20A constituting the outermost portion of the laminate sheet, an isolation metal layer 20B preventing penetration of materials, and an inner resin layer 20C for sealing.
The cathode tabs 31 and the anode tabs 32 of the stacked type electrode assembly 30 are respectively coupled to the electrode leads 40 and 41 by welding. In addition, insulative films 50 are attached to the top and bottom of each of the electrode leads 40 and 41 to prevent the occurrence of a short circuit between a thermal welding device (not shown) and the electrode leads 40 and 41 and to secure sealing between the electrode leads 40 and 41 and the battery case 20 when the upper end 24 of the case body 21 and the upper end of the cover 22 are thermally welded to each other using the thermal welding device.
In recent years, however, a new type of battery cell is required in accordance with a trend change for a slim type design or various other designs.
In addition, the above-mentioned battery cells are configured to have the same size or the same capacity to constitute a battery pack. For this reason, in order to manufacture a lightweight and thin battery pack in consideration of the design of a device, to which the battery pack is applied, it is necessary to reduce the capacity of the battery pack or modify the design of the device such that the size of the device is increased. Furthermore, electrical connection is complicated during modification of the design of the device with the result that it is difficult to manufacture a battery pack satisfying desired conditions.
Therefore, there is a high necessity for a battery cell that can be used depending upon the shape of a device, to which a battery pack is applied, while maintaining the capacity of the battery pack, and a battery pack including the same.